7. sensory motor intergration PDF

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Summary

Brain mechanisms involved in simple taskSimple task = Eating a chocolate1. Looking at and identifying the object Analyzing a visual scene by looking at the box The cornea and the lens focus an image (inverted) on the back surface (retina) of your eye. Retina has photosensitive cells Muscles control ...

Description

Brain mechanisms involved in simple task Simple task = Eating a chocolate

1. Looking at and identifying the object -

Analyzing a visual scene by looking at the box -

The cornea and the lens focus an image (inverted) on the back surface (retina) of your eye. -

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Retina has photosensitive cells

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Muscles control the shape of the lense (for focusing on diff objects)

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Muscles (protective reflexes) to open or close

Its an inverted image is projected to the back of the eye

Photosensitive cells -

Specialised cells in the retina (cones and rods) -

Rods = highly sensitive in low light conditions

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Cones = color perception -

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The neural machinery is just forward of the retina

Transduce the physical energy of light into a depolarization of the retinal ganglion cells -

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3 types of cones w/ diff spectral and sensitivities

Results in a train of action potential in the optic nerve.

The sensory receptors, rods and cones are hyperpolarized by light -

Have a resting potential closer to 0mv than most neurons.

2. Making eye movement Optic nerve -

The optic nerves project into the brain to the lateral geniculate nucleus (in the thalamus) -

Thalamus = relay nucleus -

Relay sensory info (aka pass on sensory info)

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Output ray relay in the motor system

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Relay between different cortical nucleus

Then back to the primary visual cortex (in the back of the occipital lobe)

The way visual projection works -

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Optic nerve fibered from the nasal half of the retina cross the midline projecting contralaterally (the red and blue line from the middle of the eyes) -

The lef visual world (the left side of both eyes)-> projects to the right primary visual cortex (in the occipital lobe)

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The right visual world (right side of both eyes) -> projects to the lef primary visual cortex (in the occipital lobe)

Images from the temporal half of the retina are ipsilaterally projected (on the same side) (red and blue line from the outer sides of the brain) -

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This means, if there was a damage on 2 (from diagram), you would lose peripheral vision

Since mammals have forward facing eyes, they have good stereoscopic vision -

Two eyes see things from slightly different viewpoints, the brain makes calculations which helps us understand depth on the bases on the disparity (diff between the two images) -

So damage on 1 (from the diagram) = loss of depth perception because one eye cant see shit.

3. Making a choice between possible targets Dorsal stream = Where they are

Ventral stream = What the objects are

Main stream -

Retina -> latero genetic nucleus -> primary visual cortex -> either -

Dorsal stream => posterior parietal cortex

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Ventral stream => inferotemporal cortex

Alternative stream involved in Eye movements -

Retina-> Superior colliculus (SC) -> pulvinar nucleus -> posterior parietal cortex

4. Identifying it as a chocolate, remembering where it came from -

The projections from dorsal and ventral streams -> parietal and temporallobe structures. = identifying and remembering where it came from

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The projections from brain stem -> cortex = maintaining attention and arousal like processes

5. Performing the action : making eye movements -> making a saccade (primary) motor cortex stip at back of the frontal lobe -

Frontal eye field = voluntary imagined movements

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Superior colliculus = making eye movements to a certain area Supplementary area (and the premotor area) are rostral to motor cortex = planning movements Frontal eye fields have = voluntary control of gaze direction

Basal ganglia -> movement control The basal ganglia include the caudate nucleus, putamen, globus pallidus and the substantia nigra.

Saccades require disinhibition of superior colliculus While eye movements occur, the caudate and superior colliculus fire cells. -

However, the substrannigra has been firing cells a bunch in the background and pauses when the eye moves (aka when the others fire their cells)

CSTC loops : Cortico-striato-thalamo-cortical loops Building blocks of neural-organisation in the mammalian brain Oculomotor loop (associated w/ eye movement) and Motor loop ( -

Cortical input -> Striatum -> Pallidum -> Thalamus then back to cortical input.

Cortico-straito-thalamo-cortical (CSTC) loops

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Both loops have additional cortical output to brainstem motor control areas which, for the oculomotor loop, include the superior colliculus.

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Three further loops connect cortical areas involved in cognition and emotion with the basal ganglia.

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The function of the basal ganglia in relation to motor control -

o initiation and termination of actions

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selection of actions

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relating actions to reward or reinforcement value

Reaching- muscle contraction -

Acetylcholine is released at the muscle end plate, binds to nicotinic receptors, opening sodium channels. The muscle membrane becomes depolarised close to the end plate and the depolarisation is transmitted along the membrane.

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Depolarisation and sodium influx releases stored calcium ions within the muscle and directly triggers contraction of the muscle fibre

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Sherrington, writing in the 1920’s, was responsible for the initial concept of a “motor unit”. -

It consists of the motor neuron and the set of muscle fibres which it innervates. Muscle contraction involves a mix of recruitment (of additional motor units) and rate coding (increasing the degree of contraction of a motor unit by increasing the firing frequency of the motor neuron).

Effects of TMS during a reaching task -

Deliver low amplitude transcortical magnetic stimulation (TMS) to the motor cortical hand region at different points during the reach sequence.

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Disrupts neuronal firing.

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Muscles involved in grasp become more sensitive in late stages - probably additive effect with the increased sensitivity of cortical cells to tactile input.

Taste -

The brain contains a ‘reward’ or ‘reinforcement’ system that “brings us back for more”.

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Key structures include the ventral tegmentum and nucleus accumbens.

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It is likely that the taste, texture and smell of the chocolate contribute to its rewarding properties and stimulate this brain system.

Function of basal ganglia -

Initiation and termination of actions -

Hard to start running and hard to stop running

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Selection of one action over another

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Relating actions to reward or reinforcement value

6. Performing the action : Hand movements -> picking up the chocolate Penfield’s motor homunculus As mapped by electrical stimulation of the human motor cortex. The place that takes the most energy = (in order) 1. Toe 2. Hand 3. Face 4. Jaw 5. Tongue 6. Lateral fissure

Muscle contraction Neurotransmitter = acetylcholine -> has nicotinic receptors -> opens sodium channels -> depolarises the muscle membrane -> releases calcium ions -> triggers contraction of muscle fibre.

Motor unit One motor neuron can control a bunch of muscle fibers Rate coding If acetylcholine is released rapidly = more contraction Different motor neurons can be recruited at diff times -

Control a very large group of muscle units and some control v small group.

Summary Simplest voluntary action = the integration of a large number of brain areas and systems Visual info projects via retina and lateral geniculate to visual cortex then on to dorsal and ventral processing stream Motor responses involve coordinated action of cortex and striatum (CSTC loops) + cerebellum Reward or reinforcement related processes also provide an important component of the planning and execution of action....